<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>圆的面积</title>
</head>

<body>
  <script>
    //1.输入圆的半径
    let r = prompt("请输入圆的半径：")
    //2.计算园的面积
    let result = 3.14 * r * r
    //3.输出结果在屏幕上
    document.write("圆的面积为：" + result)
  </script>
</body>

</html>